The Interior Gateway Protocol (English: Interior Gateway Protocol, IGP for short) is a protocol used for exchanging routing information between gateways (a host and a router) on an autonomous network. The routing information can be used by the Internet Protocol (English: Internet Protocol, IP for short) or another network protocol, to describe how route transferring are implemented.
A premise for the IGP protocol is that an IP address is set for each interface of each router. The router is a forwarding device for forwarding an IP packet. Before the IGP protocol is used, various parameters need to be set on the router. For example, in a typical IGP protocol, namely Open Shortest Path First (English: Open Shortest Path First, OSPF for short), a process number, a router identifier (RouterID), an area identity (area-id), an associated IP, a wildcard mask, and the like need to be configured on a router.
The IGP routing protocol includes the following content: Each router periodically sends interface information (which includes a link cost value) of the router to a peripheral device, and also forwards interface information sent by another router. After information about each router is sent to all other routers on a network, each router calculates a structural topology diagram of an entire network. Each router calculates a shortest-path tree between the router and any other known node (that is, a network segment of each interface of the router) by using the router as a root according to the network structural topology diagram of the router and generates a routing table. Index entries of the routing table are all network segments learned in an information exchange process, and a forwarding entry corresponding to each network segment is filled in according to an outbound interface and a next hop that are indicated by a topology of the tree. Therefore, a possible IP routing table entry includes a destination IP address, a next-hop IP address, and a next-hop outbound interface of a packet.
When the network topology changes, for example, when a link is disconnected, the foregoing steps are repeated to recreate a routing table entry.
It can be learned from the foregoing description that, in a manner of creating the routing table by using the IGP routing protocol, many parameters need to be configured on each routing node. For example, a process number, a router identifier, an area identity, an associated IP, a wildcard mask, and the like need to be configured on the router.